On the anomalous peak and negative capacitance in the capacitance–voltage (C–V) plots of Al/(%7 Zn-PVA)/p-Si (MPS) structure

Abstract

The frequency and voltage dependence of the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of the Al/(%7 Zn-doped PVA)/p-Si (MPS) structure were investigated in the wide range of frequency and voltage. Frequency and voltage dependence of C and G/ω shows that these parameters are functions of frequency and voltage. The C–V plot has an anomalous peak and an intersection/crossing point around 1.4 V after which C becomes negative. This negative capacitance (NC) phenomena was attributed to the surface states (Nss), series resistance (Rs) and minority carrier injection. The intensity of NC decreases with increasing frequency and the minimum value of C corresponds to the maximum value of G/ω at strong accumulation region. Whereas the C–V plots have only one peak at low frequencies, they have two peaks at high frequencies due to the special density distribution of Nss and their relaxation time. In addition, the changes in the C and G/ω were attributed to the increase in the polarization and the increased number of carriers in the structure. Impedance method was used for calculation of Rs whereas Nss was obtained using two methods; (i) the high–low frequency capacitance and (ii) Hill-Coleman method as a function of voltage and frequency, respectively. The Fermi energy level (EF), the concentration of doping acceptor atoms (NA) and barrier height (ΦB) values were obtained from reverse bias C−2 vs V plots for each frequency.